The present invention relates to weather resistant panels. In particular, the present invention relates to weather resistant doors and most particularly temperature resistant doors. For ease of reference the term xe2x80x9cpanelxe2x80x9d when used herein shall include xe2x80x9cdoorxe2x80x9d. Whilst the invention will be described with particular reference to the panel being a door, it is also applicable to other panels such as, for example, false walls, wall facias, office dividers and the like.
By xe2x80x9cweather resistantxe2x80x9d we mean that the panel is resistant to damage caused by climatic features such as temperature and humidity. In particular we mean damage that is caused by changes in climatic features and in particular changes in temperature. In addition, we mean damage that is caused when opposed faces of the panel are exposed to different climatic features in particular different temperatures.
Where the panel is, for example, an exterior door, the external face of the door may be exposed to high temperatures during the summer months whilst the internal face of the door is exposed to cool temperatures caused by, for example, air conditioning. In contrast, in the winter months the outer face of the door is exposed to cold temperatures whilst the inner face is exposed to warmer temperatures due to heating inside the building. The door will also be exposed to different temperatures during a 24-hour period as the ambient temperatures change or as a result of being exposed to direct sunlight and then in shade. Even where the panel is for use internally, the panel may be exposed to different temperatures during a period as heating is switched on and off, is altered over time or differs between rooms.
Damage to the panel caused by these differences in temperature and/or humidity includes crack failure on the surface of the panel, the development of curvature, known as xe2x80x9cbowingxe2x80x9d or other distortion of the entire surface of the panel. Distortion of a panel, such as a door, may have several severe consequences. First the appearance of the door may be marred. Secondly, the ease of the operation of the door may be affected, in particular it may become difficult to open or shut the door.
Most seriously, the air-tightness, water-tightness and sound insulation of the door may be reduced.
It is therefore desirable to provide xe2x80x9cweather resistantxe2x80x9d panels which are able to withstand these changes in temperature and/or humidity and which therefore have a longer useful life. Further it is advantageous if the panel exhibits an ability to insulate the face of the panel remote from a heat source from the heat. That is to say the panel reduces the transmission of heat through the panel.
Panels which are resistant to the transmission of heat have various applications. Heat resistant panels are desirable for use in domestic, industrial and commercial buildings and are required in buildings that have multiple occupancy such as hospitals, residential homes, offices and the like. These panels may be for internal or external use. Many countries set minimum safety requirements which building materials must meet before they can be used in the aforementioned situations. The ability of the panels to not only retard heat transmission but also to withstand changes in ambient temperature is particularly advantageous as the frequency at which panels have to be replaced is reduced.
Panels may be made from a variety of materials. Historically, wood has been the material of choice, either used alone or glazed to allow visibility through the panel. However, wooden panels can suffer from warping and splitting when subjected to changes in temperature. In recent years it has been desirable to replace wood as the preferred material with plastics materials which are generally cheaper and easier to handle than wood.
Panels formed from plastics material often comprise a pair of vacuum formed thermoplastics skins, attached to opposed faces of a frame, eg of wood and having a core of a filler material which may be, for example, glass fibre, foamed plastics or the like. Panels of this type are difficult to manufacture and do not overcome the disadvantages of wooden panels with regard to temperature resistance. Indeed for some plastics materials the damage caused by changes in ambient temperature can be greater than for panels made from wood. In particular, panels formed from plastic materials tend to suffer from bowing when exposed to increased temperature on one side of the panel. This is believed to be due to the different levels of expansion of the plastics skins on the xe2x80x9chotxe2x80x9d and xe2x80x9ccoldxe2x80x9d sides of the panel. Since the skins are bonded at their edges to the frame, the only way in which the different levels of thermal expansion of the skins can be absorbed is by bowing.
Further, it has been difficult to obtain panels formed from plastics material which meet the heat resistant criteria set down by the legislative bodies.
We have now discovered that the above-mentioned disadvantages can be overcome and that a panel having a vacuum formed thermoplastics skin can be formed which exhibits improved resistance to bowing and which exhibits substantial heat resistance.
Thus, according to a first aspect of the present invention there is provided a panel comprising a substantially open-cell, rigid foam core and at least one vacuum formed thermoplastic skin adhesively bonded to said foam core. The at least one skin preferably comprises vinyl chloride polymer such as PVC or, more preferably uPVC. The panel preferably comprises two skins adhesively bonded to opposing faces of the panel. More preferably the panel also includes a frame or frame members which are suitably of wood.
Without wishing to be bound by any theory, it is believed that when the opposed faces of a panel according to the invention are exposed to different temperatures, the rigidity of the core, to which the heated skin is adhesively bonded, provides a counter force to the thermal effect on the skin and inhibits the skin from expanding. It is further believed that the substantial stress which would be created in the skin due to the inability to expand fully is possibly absorbed, at least to some extent, by material flow within the skin. In any event, whether or not this theory is correct, it has been found that when the skin of the panel is exposed to changes in temperature and/or humidity, cracking, bowing and other damage caused by exposure to heat are substantially reduced over what been achieved heretofore. Further the transmission of heat through the panel is also reduced.
The foam core preferably has at least one face containing pores which when the, or each, skin is in place are open to the rear face of the skin. In this arrangement, the adhesive can percolate into and key to the surface of the foam, thereby forming a stronger bond. This serves to lock the skin to the foam.
Where a panel is faced with vacuum formed plastics skins, it is difficult to provide them with the depressed zones of moulding detail which are found in traditional panelled wooden panels. This is because in order to achieve the depressed zones it would be necessary either to use preformed foamed core parts of complicated shape or to leave space behind the depressed zones empty. Both methods are disadvantageous. The first is costly and the second results in a panel having zones of weakness and an unacceptable lack of rigidity. One method of overcoming this problem is to provide the moulding detail as raised portions in the skin. However, these are not as aesthetically pleasing as the preferred depressions and further, if these are hollow, the air inside the raised portions expands when the panel is exposed to increased temperatures and the mouldings may burst.
Therefore, according to a second aspect of the present invention there is provided a moulded panel comprising at least one vacuum formed skin, having depressed zones adhesively bonded to a foamed plastics core wherein the core comprises a substantially rigid plastics foam having frangible cell walls.
By a foam having frangible cell walls we mean that under compression the foam crumbles by brittle fracture of the cell walls e.g. involving a clean fracture of the cell walls. In one aspect of the invention, such foams retain a clear and substantially dimensionally accurate imprint in the crushed zone of the object through which the compressive force is applied. In general, it is preferred that the yield strength of the foam, which in this case means the minimum force required to cause the fracture of the cell walls and for the foam to crumble, is in the range of about 100 to 140 KPa (15 to 20 lbs/sq.in) more preferably at least 200 KPa (30 lbs/sq.in), since this provides the panel with useful impact resistance. In general, for a given foam composition, the greater the density, the greater the yield strength.
By using a substantially rigid plastics foam with frangible cell walls, mouldings with depressed zones of moulding detail can be readily formed by applying the vacuum formed skin to the foam core with sufficient pressure to cause the cell walls of the foam in the areas behind the depressed zones of the skin to be fractured whereby the foam is caused to conform to the contours of the skin in those zones by controlled localised crushing. Thus, air gaps between the skins can be avoided and it is not necessary to preform the core pieces in the form of complicated shapes. This is particularly advantageous since the presence of such air gaps in prior art panels has contributed to their inability to resist changes in temperature.
It is advantageous to use an open cell foam having frangible walls as pressing a skin having depressed regions into a conventional foamed core such as of polystyrene cannot be successfully achieved because the resilience of the foam will cause distortion of the skins when the pressure is released.
Any suitable plastics foam may be used provided it is substantially open-cell and rigid. However, the foam is advantageously selected to be of a high density relative to the foamed polystyrene conventionally used, e.g. a density of 75 kg/m3 or above, since this gives a better feel to the panel and makes it sound and handle more like a conventional wooden panel. However, foams having lower densities may also be selected. Where a higher density is desirable, the foam may contain a filler, more preferably a finely divided inert and preferably inorganic solid. The filler may be selected such that it contributes to the panels ability to resist changes in temperature. In a particularly preferred embodiment, the filler is capable of absorbing moisture, e.g. as water of crystallisation.
It is believed that in prior arrangements where a closed cell foam is employed, such as a polystyrene foam, any solvent employed or moisture present during the bonding of the foam core to the skin tends to be trapped between the core and the skin. Any volatilisation and subsequent condensation of the solvent or moisture due to localised changes in temperature, for example as a result of exposure to strong sunlight and then darkness, cause high localised pressure variations which tend to lead to localised bubbling, or failure of the bond. The effect is even more marked where high temperatures are encountered. A closed cell foam may even contribute to the xe2x80x9cbowingxe2x80x9d because any air or solvent trapped in the core itself will expand when the core is heated causing the panel to bow.
Without wishing to be bound by any theory, it is believed that the reduction of bowing is assisted by use of an open cell foam in the core since gas flow is possible which reduces the localised increases in pressure. As the foam is of an open cell configuration, as the gases in cells closest to the heat source expand they flow through open pathways to adjacent cells and by this means pressure is dissipated through the panel. Further, the open cell configuration reduces the rate at which heat is passed through the panel.
Thus according to a further aspect of the present invention there is provided the use of an open cell foam as a core for a panel having at least one vacuum formed skin to improve the weather resistance of the panel.
Any suitable foam may be used for this aspect of the invention provided it is substantially open cell. A foam that has an open-cell configuration at production is particularly suitable but a foam which also has frangible cell walls is particularly preferred where the skin includes depressed areas, such as to provide a moulding effect. Where a foam of this type is used, the cell wall will fracture as pressure is placed on the foam by the application of the depressed areas of the skin. This localised increase in pressure will increase the pressure inside the cell which will cause the gases to travel through the foam and the cell to collapse thereby accommodating the depressed area of the skin.
One suitable foam is a rigid filled phenolic foam. One particularly suitable foam is that produced by effecting a curing reaction between:
(a) a liquid phenolic resole having a reactivity number (as defined below) of at least 1 and
(b) a strong acid hardener for the resole, in the presence of:
(c) a finely divided inert and insoluble particulate solid which is present in an amount of at least 5 % by weight of the liquid resole and is substantially uniformly dispersed through the mixture containing resole and hardener; the temperature of the mixture containing resole and hardener due to applied heat not exceeding 85xc2x0 C. and the said temperature and the concentration of the acid hardener being such that compounds generated as by-products of the curing reaction are volatilised within the mixture before the mixture sets whereby a foamed phenolic resin product is produced.
By a phenolic resole is meant a solution in a suitable solvent of the acid-curable prepolymer composition obtained by condensing, usually in the presence of an alkaline catalyst such as sodium hydroxide, at least one phenolic compound with at least one aldehyde, in well-known manner. Examples of phenols that may be employed are phenol itself and substituted, usually alkyl substituted, derivatives thereof provided that the three positions on the phenolic benzene ring o- and p- to the phenolic hydroxyl group are unsubstituted. Mixtures of such phenols may also be used. Mixtures of one or more than one of such phenols with substituted phenols in which one of the ortho or para positions has been substituted may also be employed where an improvement in the flow characteristics of the resole is required but the cured products will be less highly cross-linked. However, in general, the phenol will be comprised mainly or entirely of phenol itself, for economic reasons.
The aldehyde will generally be formaldehyde although the use of higher molecular weight aldehydes is not excluded.
The phenol/aldehyde condensation product component of the resole is suitably formed by reaction of the phenol with at least 1 mole of formaldehyde per mole of the phenol, the formaldehyde being generally provided as a solution in water, e.g. as formalin. It is preferred to use a molar ratio of formaldehyde to phenol of at least 1.25 to 1 but ratios above 2.5 to 1 are preferably avoided. The most preferred range is 1.4-2.0 to 1.
The mixture may also contain a compound having two active H atoms (dihydric compound) which will react with the phenol/aldehyde reaction product of the resole during the curing step to reduce the density of cross-linking. Preferred dihydric compounds are diols, especially alkylene diols or diols in which the chain of atoms between the OH groups contains not only methylene and/or alkyl-substituted methylene groups but also one or more hetero atoms, especially oxygen atoms, e.g. ethylene glycol, propylene glycol, propane-1,3-diol, butane-1,4-diol and neopentyl glycol. Particularly preferred diols are poly-, especially di-, (alkylene ether) diols e.g. diethylene glycol and, especially, dipropylene glycol. Preferably the dihydric compound is present in an amount of from 0 to 35% by weight, more preferably 0 to 25% by weight, based on the weight of phenol/aldehyde condensation product. Most preferably, the dihydric compound, when used, is present in an amount of from 5 to 15% by weight based on the weight of phenol/aldehyde condensation product. When such resoles containing dihydric compounds are employed in the present process, products having a particularly good combination of physical properties, especially strength, can be obtained.
Suitably, the dihydric compound is added to the formed resole and preferably has 2-6 atoms between OH groups.
The resole may comprise a solution of the phenol/aldehyde reaction product in water or in any other suitable solvent or in a solvent mixture which may or may not include water. Where water is used as the sole solvent, it is preferred to be present in an amount of from 15 to 35% by weight of the resole, preferably 20 to 30%. Of course the water content may be substantially less if it is used in conjunction with a co-solvent. e.g. an alcohol or one of the above-mentioned dihydric compounds where one is used.
As indicated above, the liquid resole (i.e. the solution of phenol/aldehyde product optionally containing dihydric compound) must have a reactivity number of at least 1. The reactivity number is 10/x where x is the time in minutes required to harden the resole using 10% by weight of the resole of a 66-67% aqueous solution of p-toluene sulfonic acid at 60xc2x0 C. The test involves mixing about 5 ml of the resole with the stated amount of the p-toluene sulfonic acid solution in a test tube, immersing the test tube in a water bath heated to 60xc2x0 C. and measuring the time required for the mixture to become hard to the touch. The resole should have a reactivity number of at least 1 for useful foamed products to be produced and preferably the resole has a reactivity number of at least 5, most preferably at least 10.
The pH of the resole, which is generally alkaline, is preferably adjusted to about 7, if necessary, for use in the process, suitably by the addition of a weak organic acid such as lactic acid.
Examples of strong acid hardeners are inorganic acids such as hydrochloric acid, sulphuric acid and phosphoric acid, and strong organic acids such as aromatic sulphonic acids, e.g. toluene sulphonic acids, and trichloroacetic acid. Weak acids such as acetic acid and propionic acid are generally not suitable. The preferred hardeners for the process of the invention are the aromatic sulfonic acids, especially toluene sulfonic acids.
The acid may be used as a solution in a suitable solvent such as water.
When the mixture of resole, hardener and solid is to be poured, e.g. into a mould and in slush moulding applications, the amount of inert solid that can be added to the resole and hardener is determined by the viscosity of the mixture of resole and hardener in the absence of the solid. For these applications, it is preferred that the hardener is provided in a form, e.g. solution, such that when mixed with the resole in the required amount yields a liquid having an apparent viscosity not exceeding about 50 poises at the temperature at which the mixture is to be used, and the preferred range is 5-20 poises. Below 5 Poises, the amount of solvent present tends to present difficulties during the curing reaction.
The curing reaction is exothermic and will therefore of itself cause the temperature of the mixture containing resole and acid hardener to be raised. The temperature of the mixture may also be raised by applied heat but the temperature to which said mixture may then be raised (that is, excluding the effect of any exotherm) must not exceed 85xc2x0 C.
If the temperature of the mixture exceeds 85xc2x0 C. before addition of the hardener, it is difficult or impossible thereafter to properly disperse the hardener through the mixture because of incipient curing. On the other hand, it is difficult, if not impossible, to uniformly heat the mixture above 85xc2x0 C. after addition of the hardener.
Increasing the temperature towards 85xc2x0 C. tends to lead to coarseness and non-uniformity of the texture of the foam but this can be offset at least to some extent at moderate temperatures by reducing the concentration of hardener. However at temperatures much above 75xc2x0 C. even the minimum amount of hardener required to cause the composition to set is generally too much to avoid these disadvantages. Thus, temperatures above 75xc2x0 C. are preferably avoided and preferred temperatures for most applications are from ambient temperature to about 75xc2x0 C. The preferred temperature range appears to depend to some extent on the nature of the solid (c). For most solids it is from 25 to 65xc2x0 C. but for some solids, in particular wood flour and grain flour, the preferred range is 25 to 75xc2x0 C. The most preferred temperature range is 30 to 50xc2x0 C. Temperatures below ambient, e.g. down to 10xc2x0 C. can be used, if desired, but no advantage is gained thereby. In general, at temperatures up to 75xc2x0 C., increase in temperature leads to decrease in the density of the foam and vice versa.
The amount of hardener present also affects the nature of the product as well as the rate of hardening. Thus, increasing the amount of hardener not only has the effect of reducing the time required to harden the composition but above a certain level dependant on the temperature and nature of the resole it also tends to produce a less uniform cell structure. It also tends to increase the density of the foam because of the increase in the rate of hardening. In fact, if too high a concentration of hardener is used, the rate of hardening may be so rapid that no foaming occurs at all and under some conditions the reaction can become explosive because of the build up of gas inside a hardened shell of resin. The appropriate amount of hardener will depend primarily on the temperature of the mixture of resole and hardener prior to the commencement of the exothermic curing reaction and the reactivity number of the resole and will vary inversely with the chosen temperature and the reactivity number. The preferred range of hardener concentration is the equivalent of 2 to 20 parts by weight of p-toluene sulfonic acid per 100 parts by weight of phenol/aldehyde reaction product in the resole assuming that the resole has a substantially neutral reaction, i.e. a pH of about 7. By equivalent to p-toluene sulfonic acid, we mean the amount of chosen hardener required to give substantially the same setting time as the stated amount of p-toluene sulfonic acid. The most suitable amount for any given temperature and combination of resole and finely divided solid is readily determinable by simple experiment. Where the preferred temperature range is 25-75xc2x0 C. and the resole has a reactivity number of at least 10, the best results are generally obtained with the use of hardener in amounts equivalent to 3 to 10 parts of p-toluene sulfonic acid per 100 parts by weight of the phenol/aldehyde reaction product. For use with temperatures below 25xc2x0 C. or resoles having a reactivity number below 10, it may be necessary to use more hardener.
It may be necessary to make some adjustment of the hardener composition in accordance with the nature, especially shape and size, of the mould and this can be established by experiment.
By suitable control of the temperature and of the hardener concentration, the time lapse between adding the hardener to the resole and the composition becoming hard (referred to herein as the setting time) can be varied at will from a few seconds to up to an hour or even more, without substantially affecting the density and cell structure of the product.
Another factor which controls the amount of hardener required can be the nature of the inert solid. Very few are exactly neutral and if the solid has an alkaline reaction, even if only very slight, more hardener may be required because of the tendency of the filler to neutralize it. It is therefore to be understood that the preferred values for hardener concentration given above do not take into account any such effect of the solid. Any adjustment required because of the nature of the solid will depend on the amount of solid used and can be determined by simple experiment.
The exothermic curing reaction of the resole and acid hardener leads to the formation of by-products, particularly aldehyde and water which are at least partially volatilised.
The curing reaction is effected in the presence of a finely divided inert and insoluble particulate solid which is substantially uniformly dispersed throughout the mixture of resole and hardener. By an inert solid we mean that in the quantity it is used it does not prevent the curing reaction.
It is believed that the finely divided particulate solid provides nuclei for the gas bubbles formed by the volatilisation of the small molecules, primarily CH2O and/or H2O, present in the resole and/or generated by the curing action, and provides sites at which bubble formation is promoted, thereby assisting uniformity of pore size. The presence of the finely divided solid may also promote stabilization of the individual bubbles and reduce the tendency of bubbles to agglomerate and eventually cause likelihood of bubble collapse prior to cure. The phenomenon may be similar to that of froth flotation employed in the concentration of low grade ores in metallurgy. In any event, the presence of the solid is essential to the formation of the product. To achieve the desired effect, the solid should be present in an amount of not less than 5% by weight based on the weight of the resole.
Any finely divided particulate solid which is insoluble in the reaction mixture is suitable, provided it is inert. The fillers may be organic or inorganic (including metallic), and crystalline or amorphous. Even fibrous solids have been found to be effective, although not preferred. Examples include clays, clay minerals, talc, vermiculite, metal oxides, refractories, solid or hollow glass microspheres, fly ash, coal dust, wood flour, grain flour, nut shell flour, silica, mineral fibres such as finely chopped glass fibre and finely divided asbestos, chopped fibres, finely chopped natural or synthetic fibres, ground plastics and resins whether in the form of powder or fibres, e.g. reclaimed waste plastics and resins, pigments such as powdered paint and carbon black, and starches.
Solids having more than a slightly alkaline reaction, e.g. silicates and carbonates of alkali metals, are preferably avoided because of their tendency to react with the acid hardener. Solids such as talc, however, which have a very mild alkaline reaction, in some cases because of contamination with more strongly alkaline materials such as magnesite, are acceptable.
Some materials, especially fibrous materials such as wood flour, can be absorbent and it may therefore be necessary to use generally larger amounts of these materials than non-fibrous materials, to achieve valuable foamed products.
The solids preferably have a particle size in the range 0.5 to 800 microns. If the particle size is too great, the cell structure of the foam tends to become undesirably coarse. On the other hand, at very small particle sizes, the foams obtained tend to be rather dense. The preferred range is 1 to 100 microns, most preferably 2 to 40 microns. Uniformity of cell structure appears to be encouraged by uniformity of particle size. Mixtures of solids may be used if desired.
If desired, solids such as finely divided metal powders may be included which contribute to the volume of gas or vapour generated during the process. If used alone, however, it be understood that the residues they leave after the gas by decomposition or chemical reaction satisfy the requirements of the inert and insoluble finely divided particulate solid required by the process of the invention.
Preferably, the finely divided solid has a density which is not greatly different from that of the resole, so as to reduce the possibility of the finely divided solid tending to accumulate towards the bottom of the mixture after mixing.
One preferred class of solids is the hydraulic cements, e.g. gypsum and plaster, but not Portland cement because of its alkalinity. These solids will tend to react with water present in the reaction mixture to produce a hardened skeletal structure within the cured resin product. Moreover, the reaction with the water is also exothermic and assists in the foaming and curing reaction. Foamed products obtained using these materials have particularly valuable physical properties. Moreover, when exposed to flame even for long periods of time they tend to char to a brick-like consistency which is still strong and capable of supporting loads. The products also have excellent thermal insulation and energy absorption properties. The preferred amount of inert particulate solid is from 20 to 200 parts by weight per 100 parts by weight of resole.
Another class of solids which is preferred because its use yields products having properties similar to those obtained using hydraulic cements comprises talc and fly ash. The preferred amounts of these solids are also 20 to 200 parts by weight per 100 parts by weight of resole.
For the above classes of solid, the most preferred range is 50 to 150 parts per 100 parts of resole.
Thixotropic foam-forming mixtures can be obtained if a very finely divided solid such as Aerosil (finely divided silica) is included.
If a finely divided metal powder is included, electrically conducting properties can be obtained. The metal powder is preferably used in amounts of from 50 to 250 parts per 100 parts by weight of resole.
In general, the maximum amount of solid that can be employed is controlled only by the physical problem of incorporating it into the mixture and handling the mixture.
In general it is desired that the mixture is pourable but even at quite high solids concentrations, when the mixture is like a dough or paste and cannot be poured, foamed products with valuable properties can be obtained.
In general, it is preferred to use the fibrous solids only in conjunction with a non-fibrous solid since otherwise the foam texture tends to be poorer.
Other additives may be included in the foam-forming mixture; e.g. surfactants, such as anionic materials e.g. sodium salts of long chain alkyl benzene sulfonic acids, non-ionic materials such as those based on poly(ethylene oxide) or copolymers thereof, and cationic materials such as long chain quaternary ammonium compounds or those based on polyacrylamides; viscosity modifiers such as alkyl cellulose especially methyl cellulose, and colorants such as dyes or pigments. Plasticisers for phenolic resins may also be included provided the curing and foaming reactions are not suppressed thereby, and polyfunctional compounds other than the dihydric compounds referred to above may be included which take part in the cross-linking reaction which occurs in curing; e.g. di- or poly-amines, di- or poly-isocyanates, di- or poly-carboxylic acids and aminoalcohols.
Polymerisable unsaturated compounds may also be included possibly together with free-radical polymerisation initiators that are activated during the curing action e.g. acrylic monomers, so-called urethane acrylates, styrene, maleic acid and derivatives thereof, and mixtures thereof.
Other resins may be included e.g. as prepolymers which are cured during the foaming and curing reaction or as powders, emulsions or dispersions. Examples are polyacetals such as polyvinyl acetals, vinyl polymers, olefin polymers, polyesters, acrylic polymers and styrene polymers, polyurethanes and prepolymers thereof and polyester prepolymers, as well as melamine resins, phenolic novolaks, etc.
Conventional blowing agents may also be included to enhance the foaming reaction, e.g. low boiling organic compounds or compounds which decompose or react to produce gases.
The foam-forming compositions may also contain dehydrators, if desired.
A preferred method of forming the foam-forming composition comprises first mixture the resole and inert filler to obtain a substantially uniform dispersion of the filler in the resole, and thereafter adding the hardener. Uniform distribution of both the filler and the hardener throughout the composition is essential for the production of uniformly textured foam products and therefore thorough mixing is required.
If it is desired that the composition is at elevated temperature prior to commencement of the exothermic reaction, this can be achieved by heating the resole or first mixing the resole and the solid and then heating the mixture. Preferably the solid is added to the resole just before the addition of the hardener. Alternatively, the mixture of resole, solid and hardener may be prepared and the whole mixture then heated, e.g. by short wave irradiation, preferably after it has been charged to a mould. A conventional radiant heat oven may also be used, if desired, but it is difficult to achieve uniform heating of the mixture by this means.
Preferably, the foam has a density in the range 75 to 500 kg/m3 more preferably 100 to 400 kg/m3 and most preferably 100 to 250 kg/m3. Foam cell size is also important because up to a limit the larger the size of the cell for a given density, the thicker will be the walls and hence the greater the physical strength of the foam. However if the cell size is too large, the strength begins to suffer. Preferably, the cell size is in the range of 1 to 3 mm.
Any suitable thermoplastic material may be employed to form the skins of the panels provided it is capable of being produced as a sheet which is vacuum formable. For reasons of cost, the skins are preferably formed of a vinyl chloride polymer such as PVC, more preferably u-PVC, since this is the material conventionally used; however other plastics materials such as acrylics, ABS and polymer blends may also be used.
Any suitable adhesive may be used for bonding the skins to the foam core, including moisture-curing polyurethanes, two-pack polyurethanes, solvent based adhesives and, preferably, unsaturated polyester-based adhesives. Provided an open-cell foam is employed, excess solvent or moisture is not a problem as it can be absorbed into the foam.
To give improved rigidity, in general the panel skins will be spaced not only by a foam core but also by a frame or frame members such as stiles, rails, and/or mullions. The frame members may be of wood, metal or plastics or a combination of these, e.g. metal-reinforced plastics. The plastics material may contain filler, if desired, to improve hardness and/or rigidity.
In a preferred embodiment, the foam core occupies substantially the entire volume or volumes within the frame; i.e. substantially the whole space within the panel defined by the skins and the components of the frame. It is also preferred that the foam is bonded to each skin over substantially the entire area of the foam core which is in contact with that skin, even when the skin includes one or more depressed zones, since this enhances the overall strength of the panel and the resistance to bowing.
In one preferred embodiment, the core of rigid plastics foam is in the form of one or more rectangular blocks of said foam, at least one of the skins includes one or more depressed zones and the portion of the block or blocks behind each said zone conforms to the contours of said zone as a result of selective controlled crushing of the foam in the area behind said zone.
The panel skins are made from vacuum-formable sheets. Each skin may be formed by drawing the sheet down on to a suitable mould by vacuum forming.
The doors of the preferred embodiments of the present invention, when produced using a filled phenolic foam in the core exhibit resistance to bowing or warping on heating up to about 50xc2x0 C. and even above. Without wishing to be bound by any theory it is believed that the rigidity of the foam core to which the vacuum formed skin is bonded prevents the bowing of the skin and that the normal expansion of the skin due to heat is absorbed in some other manner such as an adjustment of the thickness of the skin. In any event, bowing can be substantially eliminated in the panels of the invention. In the case of a conventional foam core, such as of foamed polystyrene, on the other hand, it is believed that the core is insufficiently strong to resist the force on the skin which causes the bowing and either the foam is torn or else it is distorted, e.g. stretched, by the bowing. It is further considered that this inherent weakness of the core is further exacerbated by heat. Thus, as the temperature to which the skin is exposed is increased, so the ability of the foam to resist the bowing force is reduced.
If it is desirable that the doors be resistant to internal movement at higher temperatures, the foam core can be treated such that it has cured fully prior to the formation of the door.
The edges of the door may be left uncovered e.g. to expose the side faces of the stiles and rails where the door contains such frame members, or the edges may be capped, e.g. with uPVC cappings which may be bonded to the skins by adhesive or by heat sealing, or with extruded metal, e.g. aluminium, sections which may be attached by any suitable means such as screws. Alternatively one or both of the skins may be formed during the vacuum forming process with lips which cover the edges of the door and hence the side faces of any stiles and rails.
The panel is preferably constructed so that it does not require the skills of a craftsman to hang in place. Thus, there is provided a weather resistant panel comprising front and back faces, top and bottom faces and two side faces wherein each side face has a channel extending therealong, each of said channels being sized to receive a longitudinal cap member.
The channel extending along each side face is preferably of the same width and depth and is preferably located centrally in the width of the side of the panel. Thus, the two sides of the panel will be the same such that, subject to any design, such as panelling, on the faces of the panel, it can be left hand or right hand hung.
Each channel is preferably of generally rectangular cross-section and the depth of the channel may be greater than the depth of a portion of the cap member which will extend into the channel. The additional depth is preferably from 2 mm to 8 mm, most preferably 5 mm.
One benefit of having this additional depth to the channel is that if when the panel is to be hung in place, it is found to be larger than the space available, the panel can readily be reduced in size by removing wood from the side faces of the panel without affecting the ability of the channel to receive the cap member.
The width of the channel is preferably from 10 mm to 40 mm, more preferably 30 mm. As has been stated, whatever the width of the channel, the channel is preferably located concentric to the side face of the door.
The door may also include channels in at least one of the top and bottom faces. These channels are also shaped to receive cap members and are preferably located concentric to the face of the door. The top and bottom channels are preferably of the same size and configuration.
A longitudinal cap member suitable for insertion in one side channel of the panel preferably comprises a pair of upper flanges in a common plane which are spaced apart and conjoined by a lower flange located beneath the pair of flanges and parallel therewith.
The combined widths of the two upper flanges and the gap between them is preferably equal to the width of the panel. The widths of the two upper flanges are preferably different. The flanges are preferably arranged such that when the cap is placed in one side channel of the panel, the lower flange is located in the channel and an upper surface thereof is collinear with the upper surface of the walls of the channel and the upper flanges extend over the upper edges of the walls of the channel. This arrangement means that a leaf of a hinge may be readily recessed in the finished panel such that it can be correctly hung in place. In order to locate the hinge, a section of one of the upper flanges may be removed such that the leaf of the hinge can lie across the upper edge of the wall of the channel and across the upper surface of the lower flange. The length of the section of the flange removed will depend on the length of the hinge.
The two upper flanges may be of different widths. This will enable the same cap member to be suitable for use with one of two different sizes of hinge. In the UK two standard sizes of hinge are commonly used with household doors, these are 30 mm and 35 mm. Thus, in a particularly preferred embodiment of the present invention the widths of the upper flanges and the spacing between them are such that the distance from the outside edge of one flange to the opposed edge of the gap between the upper flanges is 30 mm and the distance from the outside edge of the other flange to the opposed edge of the gap between the upper flanges is 35 mm.
Two legs preferably extend downwardly from the flanges and are preferably located such that in use they are a sliding fit with the inner walls of the channel in the door. They preferably extend downwardly from the flanges for a length that is less than the depth of the channel. A foot member may extend inwardly from each leg to form a ledge extending along the cap member below the plane of the lower flange. This ledge enables a plate to be located below the lower flange and spaced therefrom. When a hinge has been located on the upper face of the lower flange, it will be fixed to the lower flange, preferably by means of at least one screw. If a metal plate is located below the lower flange the, or each, screw will extend through the plate thereby strengthening the fixing of the hinge to the cap member.
As the cap member is separate from the panel, the panel fitter, can place the cap member against the panel frame to accurately note the position of the hinge before it is fitted to the door. The appropriate portion of one flange can then be removed from one of the pair of upper flanges and the hinges connected to the cap member before the cap member is inserted into one side channel in the panel. The door may then be hung in place in the conventional manner. In one alternative arrangement, the cap member having had the hinge members located on its surface may be connected to the door panel via the hinges before it is placed in the channel of the panel.
The cap member may be held in place in the channel by any suitable means. In a preferred embodiment, the cap member will be attached to the panel by means of screws.
The configuration of the cap member selected for use in the opposing side face to that carrying the hinges will depend on the type of locking mechanism to be used. Suitable locking mechanisms include conventional mortice locks and multi-point locks fitted to a groove known as a Eurogroove or any other suitable groove.
A longitudinal cap member suitable for insertion in one side channel of the panel preferably comprises a flange, preferably having a width corresponding to the width of the panel. This cap member is also suitable for use in the top or bottom channel of the panel, where present and is particularly suitable for the top channel.
Two legs preferably extend downwardly from the flange and are preferably located such that in use they are a sliding fit with the inner walls of the channel in the door. They preferably extend downwardly from the flange for a length that is less than the depth of the channel. A foot member may extend inwardly from each leg to form a ledge extending along the cap member below the plane of the flange. This ledge enables a plate to be located below the flange and spaced therefrom. This plate can be used to strengthen the attachment of the lock to the cap member.
The cap member may be provided with a plate located on the ledge.
When the panel is to be hung in place, the cap member may be held against the panel frame and the position of the lock accurately noted before an appropriate section is cut from the cap member. The cap member may then have the lock fitted before being located in the channel. The cap member will then be placed in the channel and may be fastened in place by means of screws, glue or both screws and glue.
The ledges of the above second and third aspects may be located from 0.5 mm to 2 mm below the lowest surface of the flanges, preferably 1 mm.
A longitudinal cap member suitable for insertion in one side channel of the panel preferably comprises a pair of coplanar spaced apart flanges and a trough member. This cap member is also suitable for use in the top or bottom channel of the panel, where present, and is particularly suitable for the bottom channel. When the cap member is used in a side channel of the panel it is suitable for use with a multi-point lock. If the cap member is used in the bottom channel of the panel, the trough member may include a draft excluder, such as a brush or flipper seal.
Where a panel comprises the channel and cap members described above, there is open space located around the periphery of the panel. Without wishing to be bound by any theory it is believed that the expanding gases which travel through the foam in the manner described when the panel is exposed to increased temperature vent into this void space and thus pressure at the surface of the door is reduced. Further, where the panel is a door, the cap members will include apertures for the hinges and locks allowing venting of the gases to air.
In a particularly preferred embodiment of the present invention the panel comprises a frame, having channels as described above, a foam core comprising an open cell foam of the kind described above and cap members of the kind described above. Most preferably the panel is a door.